The U.S. says there will be a "firm response" as Ukrainian forces holding ground in Russia's Kursk region now face North Korean troops "engaging in combat."

Experts tell Andy Gregory and Tom Watling that the real question is how much Kyiv’s troops are able to inflict casualties on the Russians as the price for taking the territory back

Ukrainian President Volodymyr Zelensky said Russia has deployed nearly 50,000 troops to Kursk, the southern Russian region where Kyiv launched its surprise counteroffensive in the summer.